Variable resistance shift rail detent assembly and shift control method employing same

Abstract

A mechanical transmission system (10) is provided with a detent mechanism (156/172, 186/196) for applying a selectively variable detent resistance to disengagement of an engaged gear ratio. To provide resistance to shift lever (31) induced jumpout when no intent to shift is sensed, a greater detent resistance is provided, and to provide improved shift quality upon sensing an intent to shift, a lesser detent resistance is provided. The mechanism also may be utilized to maintain the transmission in neutral.

We claim: 
     
       1. A transmission system (10) comprising a master friction clutch (14) for drivingly coupling an engine (12) to a compound mechanical transmission (16) including a main section and an auxiliary section, a shift member (150, 176) for moving a selected positive clutch member (151A) in said main section to a selected one of an engaged or a disengaged position and means (120, 146) independent of operation of said shift member and said master friction clutch for sensing a requirement to move said selected positive clutch member from said engaged position to said disengaged position and for providing an intent-to-shift signal indicative thereof, said system characterized by: a detent mechanism (156/172, 186/196) for providing a selectively variable resistance to movement of said clutch member from said engaged to said disengaged position, said detent mechanism having a first condition for providing a greater resistance to movement of said clutch member from said engaged to said disengaged position and a second condition for applying a lesser resistance to movement of said clutch member from said engaged to said disengaged position, said detent mechanism assuming said second condition upon sensing said intent-to-shift signal.   
     
     
       2. A method for controlling a transmission system comprising a master friction clutch (14) for drivingly coupling an engine (12) to a compound mechanical transmission (16) including a main section and an auxiliary section, a shift member for moving a selected positive clutch member in said main section to a selected one of an engaged or a disengaged position, means independent of operation of said shift member and said master friction clutch for sensing a requirement to move said selected positive clutch member from said engaged position to said disengaged position and for providing an intent-to-shift signal indicative thereof, and a detent mechanism for providing a selectively variable resistance to movement of said clutch member from said engaged to said disengaged position, said detent mechanism having a first condition for providing a greater resistance to movement of said clutch member from said engaged to said disengaged position and a second condition for applying a lesser resistance to movement of said clutch member from said engaged to said disengaged position, said method comprising: in the absense of said intent-to-shift signal, causing said detent mechanism to assume said first condition, and   upon sensing said intent-to-shift signal, causing said detent mechanism to assume said second condition.   
     
     
       3. The method of claim 2 wherein said means provides a signal indicative of a target gear ratio and said method further comprises causing said detent mechanism to assume said first condition upon sensing engagement of said target gear ratio. 
     
     
       4. A manually shifted change-gear transmission system comprising a master friction clutch (14) for drivingly coupling an engine (12) to a compound mechanical transmission (16) including a main section and an auxiliary section, a manually operated shift lever for moving a selected clutch member in said main section to a selected one of an engaged or a disengaged position, said transmission system comprising: means independent of operation of said master friction clutch and manual movement of said shift lever to sense an operator desire to shift said clutch member from said engaged to said disengaged position and to provide a signal indicative thereof, and   a detent mechanism for providing a selectively variable resistance to movement of said clutch member from said engaged to said disengaged position, said detent mechanism having a first condition for providing a greater resistance to movement of said clutch member from said engaged to said disengaged position and a second condition for applying a lesser resistance to movement of said clutch member from said engaged to said disengaged position, said detent mechanism assuming said second condition upon sensing said signal.   
     
     
       5. A partially automated transmission system comprising a fuel-controlled engine, an engine controller for controlling fueling of the engine in accordance with command output signals, a compound multiple-speed mechanical transmission having an input shaft driven through a master friction clutch by the engine, an output shaft, a main transmission section shifted by a manual shift lever and an auxiliary section, an operator selector movable to a first position for selection of upshifts to a target ratio and to a second position for selection of downshifts to a target ratio, and a control unit for receiving input signals and processing same according to predetermined logic rules to issue command output signals, said system characterized by: a detent mechanism for providing a selectively variable resistance to movement of said shift lever from a ratio-engaged to a ratio-disengaged position, said detent mechanism having a first condition for providing a greater resistance to movement of said shift lever from said ratio-engaged to said ratio-disengaged position and a second condition for applying a lesser resistance to movement of said shift lever from said ratio-engaged to said ratio-disengaged position, and   said logic rules being effective to determine, independently of operation of said master friction clutch and said shift lever, a driver intent to move said shift lever to said ratio-disengaged position and, upon sensing such intent, causing said detent mechanism to assume said second condition.   
     
     
       6. The transmission system of claim 5 wherein said shift lever is operable to cause axial movement of a shift rail, said detent mechanism comprising a notch in said rail and a detent plunger biased with variable force to engage said notch. 
     
     
       7. The transmission system of claim 6 wherein said notch and said plunger are provided with complementary ramped surfaces.